PHOTODYNAMIC THERAPY WITH PHOTOFRIN-II INDUCES PROGRAMMED CELL-DEATH IN CARCINOMA CELL-LINES

The mode of cell death following photodynamic therapy was investigated from the perspective of programmed cell death or apoptosis, Human pro state carcinoma cells (PC3), human non-small cell lung carcinoma (H322 a) and rat mammary carcinoma (MTF7) were treated by photodynamic thera py. An examination of extracted cellular DNA by gel electrophoresis sh owed the characteristic DNA ladder indicative of internucleosomal clea vage of DNA during apoptosis. The magnitude of the response and the ph otodynamic therapy dosage required to induce DNA fragmentation were di fferent in PC3 and MTF7. The MTF7 cells responded with rapid apoptosis at the dose of light and drug that yielded 50% cell death (LD(50)). I n contrast, PC3 showed only marginal response at the LD(50) but had a marked response at the LD(85). Thus, apoptosis did not ensue as quickl y in PC3 as in MTF7. The H322a cells were killed by photodynamic thera py but failed to exhibit any apoptotic response. The results also sugg ested that apoptosis in these cell lines has a minor requirement for d e novo protein synthesis and no requirement for de novo RNA synthesis. This study indicates that although apoptosis can occur during photody namic therapy-induced cell death, this response is not universal for a ll cancer cell lines.